I'm sure that as soon as Windows Phone increases its market share to above 40% (where both Android and iOS are at) then Stack Exchange will waste no time in developing an official app for it.
As it stands, though, Windows phone doesn't even have 4% market share in the smartphone market, so there's little reason to pursue it.
Consider bringing this topic up again once Windows phone nears or surpasses either iOS or Android.
the market share stats in the smartphone market wouldn't be same if we filter the result where job is programmer.
Fortunately for you, Stack Overflow does a user survey once a year, and already has this data. From the summary report of the 2013 survey we find the following is true about Stack Overflow Users:
What technology products do you own?
- Android phone - 63.8%
- iPhone - 30.7%
- iPad - 28.8%
- Android Tablet - 28.7%
- Windows Phone 10.3%
- Windows tablet 5.6%
If your company has a native mobile app, what platforms do you support?
- Android Phone - 39.5%
- iPhone - 37.9%
- iPad - 31.5%
- Android Tablet - 29.7%
- Windows Phone - 13.9%
(Note that the questions allowed one to choose more than one option, as many developers have multiple devices. The survey did not ask which device they used primarily.)
So you are right, developers have or own windows phone at a higher rate than the public. It's still significantly skewed towards iOS and Android, though. You could double it and it still wouldn't get close to the Android and iOS market share among Stack Overflow users.
It still doesn't justify, from a business standpoint, spending finite resources on such a small portion of the userbase when there are other projects that would more positively affect more of the users than this project.
The raw survey data is available. I don't have the time nor inclination to do further analysis, but if you want to bolster your argument, consider taking data from the survey for top users and see what devices top users have.